HHLA2 and clear cell renal carcinoma: The positive rate of HHLA2 expression in ovarian cancer tissues in the current study was 17.2% (11/64), which was considered a low percentage compared with 61 ~ 66% in NSCLC [11, 21], 47.6% in colorectal cancer [16], 50% in clear cell renal cell carcinoma [15], and 56% in triple-negative breast cancer [8].